1. Field of the Invention
The present invention relates to the scheduling of service in a mobile communication system. More particularly, the present invention relates to the scheduling of service based on a delay in a network.
2. Description of the Related Art
Voice communication between users of mobile communication terminals has been provided for many years by various service providers. As use of mobile communication terminals has become more widespread, mobile communication terminal users now desire advanced services such as email, Internet access, video streaming, real time gaming, and the like. One technology that is under development to provide such advanced services is the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system. A goal of the LTE system is to provide advanced services with a download speed of 100 Mbps.
To provide such advanced services at high speed, the LTE system associates a Quality of Service (QoS) parameter with a service provided to a user. For example, the LTE system may assign a first QoS to a mobile communication terminal that is participating in a voice communication and assign a second, higher QoS to a mobile communication terminal that is receiving a streaming video. The LTE system makes scheduling decisions based on the QoS assigned to each mobile communication terminal.
FIG. 1 illustrates components of an LTE system providing a service to a user according to the conventional art.
Referring to FIG. 1, an LTE system includes a Packet data network GateWay (PGW) 110, a Serving GateWay (SGW) 120, an evolved Node B (eNB) 130 and a User Equipment (UE) 140. The PGW 110 and the SGW 120 are located together at a Mobility Management Entity/GateWay (MME/GW, not shown) that is located remotely from the eNB 130. The PGW 110 provides an interface between the MME/GW and a Packet Data Network (PDN) (e.g., the Internet, not shown) and the SGW 120 provides an interface between the MME/GW and one or more eNBs (e.g., eNB 130) served by the MME/GW. Between the PGW 110 and the SGW 120, a Core Network (CN) 150 is provided for transmitting and receiving information between the PGW 110 and the SGW 120. Between the SGW 120 and the eNB 130, a Backhaul Network (BN) 160 is provided for transmitting and receiving information between the SGW 120 and the eNB 130. The Backhaul Network 160 typically comprises an S1 connection. Finally, the eNB 130 provides a wireless service to the UE 140.
When a packet-based service, such as a data service, is provided to the UE 140 in the LTE system, a Packet Delay Budget (PDB) is associated with the UE 140 depending on the QoS of the service. More specifically and with reference to Table 1, each Service Data Flow (SDF) that may be provided to the UE 140 is assigned a QoS class Identifier (QCI) and each QCI has a corresponding PDB. The PDB is an allowed delay time between the PGW 110 and the UE 140 and defines an upper bound of time-delay that a packet can experience between the PGW 110 and the UE 140. The QCIs, and PDBs associated with each QCI, are defined in 3GPP Technical Specification 23.203, the entire disclosure of which is hereby incorporated by reference. In Table 1, PELR indicates Packet Error Loss Rate, and GBR indicates Guaranteed Bit Rate.
TABLE 1QCIResource TypePriorityPDBPELRExample Service1GBR2100ms10−2Conversational Voice24150ms10−3Conversational Video (LiveStreaming)3350ms10−3Real Time Gaming44300ms10−6Non-Conversational Video(Buffered Streaming)5Non-GBR1100ms10−6IMS Signaling6630ms10−6Video (Buffered Streaming)TCP-based (e.g., www, e-mail,chat, ftp, p2p file sharing,progressive video, etc.)77100ms10−3Voice,Video (Live Streaming)Interactive Gaming88300ms10−6Video (Buffered Streaming)99TCP-based (e.g., www, e-mail,chat, ftp, p2p file sharing,progressive video, etc.)
In the LTE system of FIG. 1, the eNB 130 schedules a service to the UE 140 as well as other UEs supported by the eNB. To schedule the services to the UEs, the eNB 130 uses an algorithm to determine a QoS scheduling metric for each SDF provided to respective UEs. The scheduling metric is defined in Equation (1).
                                          S            k                    ⁡                      (            t            )                          =                                            C              ⁡                              (                                                                            R                      k                                        ⁡                                          (                      t                      )                                                                                                  AvgR                      k                                        ⁡                                          (                      t                      )                                                                      )                                      ⁢                          (                                                                    D                    k                                    ⁡                                      (                    t                    )                                                                    T                  k                                            )                                +                      O            ⁡                          (                              P                k                            )                                                          Eq        .                                  ⁢                  (          1          )                    
In Equation (1), t is a subframe number, Sk(t) is the QoS scheduling metric for each SDF at subframe t, C is a constant, Rk(t) is a channel capacity at t, Avg Rk(t) is an average channel capacity at t, Dk(t) is a packet delay for a non-Guaranteed Bit Rate (non-GBR) service at t or a token delay for a GBR service at t, Tk is the PDB of service k and O(Pk) is an offset according to the priority of service k. Accordingly, the result Sk(t) of the scheduling metric is dependent on the value of Tk, wherein Tk is the PDB corresponding to the service provided to the UE.
After determining Sk(t) for the UEs served by the eNB, the eNB selects the largest scheduling metric for radio resource allocation per subframe. The selection is made according to Equation (2).K=arg max Sk(t)  Eq. (2)
In the above described LTE system, scheduling is determined by the eNB using Equations (1) and (2) which are dependent on the PDB associated with the service provided to the UE. In this case, the scheduling metric does not consider actual delays between the PGW and the UE.
FIG. 2 illustrates components of an LTE system and their associated delays according to the conventional art.
Referring to FIG. 2, packet data, related to a service that is provided to the UE 140, is received at the PGW 110 and transmitted to the UE 140 through the Core Network 150, the SGW 120, the Backhaul Network 160 and the eNB 130. While there are several sources of delay in the packet data stream, two delays of concern are the Core Network delay (CN delay) 210 and the Backhaul Network delay (BN delay) 220. The CN delay and BN delay are cumulatively referred to as the CB delay.
During operation of the LTE system, the CB delay varies depending on data traffic and other conditions of the system. Typically, the CB delay is considered to have a value between 10 ms and 50 ms, depending on system parameters such as proximity of the eNB to the MME/GW. However, an actual CB delay is not considered by the eNB when performing the scheduling of services. That is, by using Equation (1), the scheduler of the eNB 140 only considers the assigned PDB (i.e., Tk) associated with the SDF as listed in Table 1 when determining Sk(t).
In the above LTE system, a situation may occur in which, given close proximity of the eNB to the MME/GW, light data traffic, or other such conditions, the CB delay may be small. However, because the actual CB delay is not considered when determining the scheduling metric, the eNB may erroneously determine that service cannot be provided to a UE since scheduling is determined based on the assigned PDB. In this situation, channel utilization will not be maximized because available resources will not be used to provide the desired SDF to the UE.
Therefore, a need exists for an improved apparatus and method for determining transmission delay in a mobile communication system and scheduling service based on the determined delay.